Electrical relay



Oct 26, 1954 c. s. sNAvELY 2,692,927

ELECTRICAL RELAY Filed Jan. 5, 1952 3 Sheets-Sheet l 1^, 42 a1 IIT 24a6b 6a H15' A TTRIYE'Y DCL 26, 1954 c. s. slNAvELY 2,692,927

ELECTRICAL RELAY Filed Jan. 5, 1952 3 Sheets-Sheet 2 Insulalz'on l IN VEN TOR.

@lare/nc@ S, Smlvely BY HIS ATTRTY Oct. 26, 1954 C. s. sNAvELY 2,692,927

ELECTRICAL RELAY Filed Jan. 5, 1952 3 sheds-sheet :s

Fig IN1/EN TOR. v

Clarence S. Snavely w. km.

HIS A TTORNEY Patented Oct. 26, 1954 ELECTRICAL RELAY Clarence S.Snavely,

to Westinghouse Miami Shores, Fla., assigner Air Brake Company,Wilmerding, Pa., a corporation of Pennsylvania Application January 5,1952,

18 Claims.

My invention relates to electrical relays, and particularly toelectrical relays responsive to relatively high currents which prohibitthe use of the usual relay magnetizing windings.

Load circuits carrying direct current cf several thousand amperesrequire conductors of very large cross-sectional area to handle suchload currents safely and without excessive heat and voltage losses. Suchheavy conductors, or bus bars, are not adapted for winding the usualtype of meter or relay coils. To measure the high current flow in aconductor of large cross-sectional area, meters are sometimes used whichare connected in shunt with a portion or section of the conductor havinga known resistance. Meters which are shunt connected to the conductorshave been used to initiate various control functions in response topredetermined values of current fiowing through the conductors, themeters being provided with electrical contacts which are operated at thepredetermined values of the load current.

In other control applications it has been found desirable to provide arelay mechanism for a conductor or bus bar of large cross-sectionalarea, which relay mechanism is operated by the magnetic iiuX due to thecurrent ilow through the conductor, the relay mechanism being operatedat a predetermined value of the load current. A bus bar relay mechanismof this type is illustrated and described in my copending applicationfor Letters Patent of the United States, Serial No. 771,024, led onAugust 28, 1947, for Electrical Relays, now Patent No. 2,584,749 issuedFebruary 5, 1952.

The relay mechanism disclosed in my copending application provides tworelay structures mounted in housings of conducting material, the twohousings being bolted together back-to-back to form a conducting path ofsuitable cross-sectional area to carry the heavy load currents of thecircuit into which the relay housings are connected. In the relaymechanism disclosed in the aforesaid application, a high release to pickup ratio is obtained by features of construction described in saidapplication, a change in the release to pick up ratio being obtained byadjustments in the magnetization of the permanent magnet provided forthe relay mechanism.

It is an object of my present invention to provide a self-containedrelay unit adapted to be clamped to a conductor or bus bar of largecrosssectional area carrying heavy load currents and operable by themagnetic iiux due to the Current flow in the conductor cr bus bar.

Serial No. 265,135

Another object of my invention is to provide a relay mechanism having ahigh release to pick up ratio wherein mechanical means are incorporatedto vary the release to pick up ratio of the relay.

These and other objects of my invention I accomplish by providing anonmagnetic metal frame or support secured to a base of insulatingmaterial for mounting the magnetic and contact structures of the relaymechanism. The insulating base together with a backstrap cover also madeof insulating material, form a clamping means whereby the relaymechanism is secured to a conductor or bus bar.

A one-piece molded rotor of insulating material is pivotally supportedin the nonmagnetic frame, the rotcr having molded therein a magnetizablearmature and spring contact lingers, the spring contact ngers coactingwith stationary contacts secured to the insulating base. The nonmagneticframe of the mechanism also supports two magnetizable cores, the ends ofwhich extend through the insulating base and through slots or openingsprovided in the associated conductor or bus bar. The cores together withthe armature and a backstrap complete the magnetic circuit for therelay, the conductor or bus bar being enclosed by the magnetic circuit.

The armature supporting rotor of the relay mechanism is provided with aspiral return spring, one end of which is secured to the rotor while theother end is secured to an adjustable arm. By means of an adjustingscrew coacting with the adjustable arm, the tension of the spiral returnspring may be increased or decreased. The tension of the spiral returnspring determines the pick up value of the relay.

The rotor is further provided with two diametrically oppositelyextending flat springs, the outer or free ends of the springs beingreceived in slots cut into two ears or tabs of insulating material. Thetabs or ears are secured to two tapped blocks threaded respectively onthe oppositely threaded ends of a long screw confined by the nonmagneticframe. By turning the long adjusting screw, the insulating tabs or earsare moved toward and away from each other. The varying of the eiiectivelength of the two flat springs in this manner varies the stiffness ofthe ilat springs. The adjustment of the long screw controls the ratio ofthe release to pick up value of the relay.

I shall describe one form of apparatus embodying my invention and shallthen point out the novel features thereof in the appended claims.

In the accompanying drawings, Fig. 1 is a side elevational view of mynovel relay clamped to a bus bar. Fig. 2 is a sectional view taken alongthe line II-II of Fig. l. Fig. 3 is a plan view of the relay mechanismwith the cover removed and portions of the frame broken away. Fig. 4 isa sectional view taken along the line IV--IV of Fig. 3. Fig. 5 is aperspective view of the relay operating mechanism with portions brokenaway, while Fig. 6 is a perspective view of the relay rotor assembly,portions of the rotor being broken away to show details of construction.

Similar reference characters designate similar parts throughout theseveral views.

Referring now in detail to the drawings, the reference character ldesignates in general a relay mechanism embodying my invention securedto a bus bar 2. The bus bar 2 is of a highly conductive, nonmagneticmaterial adapted to be connected in series with a load circuit (notshown) carrying several thousand amperes of direct current, by vway oftangs 2a. The bus bar 2 is provided with two openings, or slots, 2b cutinto the opposite edges of the bar, the slots leaving a central portion'ic of reduced cross-sectional area which conducts the entire loadcurrent through the magnetic structure of the relay mechanism l which Iwill now describe.

The relay mechanism l comprises a base plate 3 of insulating materialformed with a suitable rectangularly shaped recess 3a in its uppersurface and having molded therein two pairs of adjustable contacts; apair of front contacts da and a pair of back contacts lib. The front andback contacts la and 4b are connected by way of connectors 5 to theterminal posts 5a and (ib, respectively, molded in the base plate 3.Secured within the recess 3a of the base plate is a nonmagnetic frame orbracket 'i comprising a base la and four integral standards lb-le, i

the frame being secured to the base plate 3 by nonrnagnetic screws 8recessed in the underside of the base plate. Fixed to the upper ends ofthe legs Eb-le of the frame l by four nonmagnetic screws 9 is anonmagnetic plate lil formed with a dependent circular boss ict (Fig.Li). The boss ma is provided with a concentric journal opening lb whichis in vertical alignment when plate it is secured to the frame legs,with a similar opening 'if provided in the frame base la.

Secured in the base la of the nonmagnetic frame l are two magnetizablecores il and l2 extending downwardly with some clearance throughsuitable openings 3b provided in the insulating base plate 3. withenlarged upper ends of pole Vpieces ila and lZa, respectively, a portionof each of the pole pieces being milled away to form vertical pole facesHb and |213 on the respective pole pieces. It will be noted in Fig. 3that the vertical pole faces are parallel to each other, but angularlydisposed with respect to the plane intersecting the axes of the two polepieces.

Rotatably mounted in the nonmagnetic frame 1 for oscillation about avertical axis is a rotor assembly I3 (Fig. 6) comprising a molded rotorill of insulating material having molded therein a vertical shaft l5 anda magnetizable armature I6. In the construction of the rotor assembly,the shaft i5 is press tted into an opening (not shown) in the center ofthe armature It before the rotor is molded. The shaft may be of asuitable magnetizable metal or it may be of a metal having the leastbearing friction and wear. I thus provide a single shaft The cores areformed for the rotor assembly for accurate alignment of the rotor and alow reluctance armature intersecting the shaft at right angles. The endsof the armature are formed with vertical pole faces I6@ and leb, theplanes of the pole faces (Fig. 3) being angularly disposed with respectto the longitudinal axis of the armature. As will hereinafter appear,the armature pole faces ita and Ib are so formed and the armature somounted in the rotor assembly that the armature pole faces will beparallel with the pole faces Hb and 12b of the pole pieces when thearmature is in its midstroke position.

Four spring fingers il-Zi are also molded in the rotor ifi in the sameplane with the armature i6 but normal thereto, the fingers beingarranged in coextensive parallel pairs extending in opposite directionsfrom the rotor. Molded in the rotor in the central portion thereof aretwo diametrically oppositely extending flat springs 2i and 22, the natsprings being slightly longer than the spring contact fingers Ms, andextending in the same directions. The flat springs 2i and '22 inaddition to serving as a biasing means for the rotor itl as willhereinafter be described, also serve as the heel connection for thespring contact fingers Il-Zli. The outer or free ends of the flatsprings 2l and 22 are electrically connected by way of connectors 23 tothe terminal posts 2da and 2Gb, respectively, molded in the base plate3. As will hereinafter appear, there is very little exing of theconnectors 23 because the free ends of the springs 2i and 22 are heldpractically stationary. The inner ends of the springs 2! and 22 moldedwithin the rotor are electrically connected to the inner ends of thespring contact fingers, the fiat spring 2i being connected to thecontact ngers il and is by conducting strips 25 (Fig. 6) riveted to saidspring and fingers, while flat spring '22 is similarly connected to theContact fingers le and 2li.. A slot or groove 26 is provided in theupper surface of the rotor member for receiving the inner end of a coiltension spring 2l, the coils of which encompass the upper end of therotor la.

The rotor assembly i3 is mounted within the frame l with the lower endof shaft i5 in the bearing provided by opening lf in the base 'ia andthe upper end of the shaft in the bearing formed by the opening im? inplate i@ when said plate is secured to the frame legs. The rotorassembly I3 is adapted to be oscillated about a vertical axis defined bythe shaft i5 in a manner to be described, the armature being oscillatedin the plane of the pole faces Hb and |219 of the pole pieces and thecontact fingers [Lfd being oscillated in the plane of the stationarycontacts da. and lib.

Adjustable means are provided for varying the tension of the coil spring2l to bias the rotor assembly i3 to one extreme position in which theback contacts 1lb are engaged by the spring ccntact fingers i7 and is ofthe rotor assembly. The tension of the coil spring `2l will determinethe flux level o-r current value at which they baci; contacts 1lb aredisengaged and the front contacts da engaged by the spring contactfingers I8 and 20.

To this end an arm 28 is pivoted on the dependent boss lila of the frameplate lil (Figs. 4 and 5), the free end of the arm being formed with adependent ear or abutment plate 29 which is riveted to the free end ofthe coil tension spring 2l of the rotor assembly. Coacting with theabutment plate 29 of the arm 28 is an adjusting screw 30, threadedthrough an ear 'Ig offra-me leg lb, the inner end of the screw abuttingthe plate 29 (Figs. 3 and 5). By threading thescrew 3c inwardly, the arm2t is pivoted in a counterclockwise direction (Fig. 3), therebyincreasing lthe bias of the coil tension spring. To decrease the bias ofthe coil tension spring the adjusting screw is threaded outwardly of ear1g.

The bias of the coil tension spring 2l tends to rotate the rotorassembly I3y in a counterclockwise direction (Fig. 3,) To limitv theangular displacement of the rotor assembly I3 due to the bias of thecoil tension spring, nonmagnetic stop screws 3Ia and 3Ib are threadedthrough thev frame legs 'Ib and 1d, the inner ends of which are adaptedto abut the armature I6 in one extreme or release position in which theback contacts 1lb-Il and IIb-I9 are closed. It will be noted in Fig. 3that in the release position of the armature I6 a small air gap existsbetween the pole faces I Ib and I2?) of the pole pieces and the polefaces ISU. and Ib of the armature. rlhe two sets of pole faces arepractically parallel in the release position of the armature, the polefaces of the armature and pole pieces being so constructed and assembledthat the two pairs of pole faces will be parallel when the armature isin its mid stroke position. To limit the rotation of the rotor assemblyin a clockwise direction, nonmagnetic stop screws 32a and 32D arethreaded through the legs lc and le, respectively, of the frame l; theclockwise rotation of the rotor assembly being limited to a secondextreme or full-stroke position in which the front contacts la-I8 and411-20 are closed and the air gaps between the armature pole faces irt,Ib and the pole faces IIb, I2b of the pole pieces are very nearlyclosed. It will be appreciated that abutment of the pole faces should beavoided to prevent sticking of the armature when magnetic flux threadingthe armature decays.

The relay mechanism thus far described is mounted on the` bus ,bar 2,the insulating base plate S engaging the top surface of the bus bar andthe cores II and I2 extending into and through the bus bar slots v2b.The cores II and I2 are enclosed in sleeves 33 of insulation material(Fig. 2) to insulate the cores from the bus bar. It will be noted inFig. 2 that the lower ends of the cores extend slightly below the bottomsurface of the bus bar. A backstrap 34 of magnetizable material isprovided for the lower ends of the cores iI and I2 to complete themagnetic circuit of the relay. The backstrap 34 is enclosed by abackstrap cover 3'5 made of insulation material which also serves as aclamping means for securing the relay mechanism I to the bus bar 2.

The backstrap cover 35 is clamped to the underside of the bus bar 2 bymeans of four screws 36k preferably made of brass. The heads of thescrews 3E are recessed in suitable openings 3c provided in theinsulating base plate 3, the screws passing through openings 2d in thebus bar 2 with some clearance, and are threaded into metal inserts 3l'recessed in the backstrap cover 35. A strip 33 of insulation material isinterposed between the bottom face of the bus bar and the backstrapcover, the strip being suitably pe forated to accommodate the cores Iland I2, and the clamping screws 35.

The bacastrap cover is formed with a recess 35a to accommodate the endsof the cores I I and I2 and the magnetizable backstrap 3,4. Thebackstrap S4 is biased upwardly against the lower ends of the cores by aleaf spring 39 interposed between the backstrap and the bottom of therecess 35a. One or more nonmagnetic shims 4I) may be inserted betweenthe lower ends of the pole pieces I I and I2 and the baclrstrap 34 tovary the reluctance of the magnetic circuit of the relay, whereby anapproximate pick up value of flux may be obtained at which the relaywill close its front contacts.

A cover III preferably of sheet steel, secured to the top plate IIJ ofthe frame by two screws 42 and having a gasket 43 (Figs. 3 and 4)interposed between the lower edge of the cover and the base plate 3,seals the relay mechanism against the entry of foreign matter, the steelcover acting as a magnetic shield for the relay structure.

The relay mechanism thus far described will operate to open its backcontacts 4in-Il and IIb-I9 and close its front contacts lla-I8 andIla-*20 in response to a now of current of predetermined value throughthe bus bar 2. The flow of direct current through the bus bar creates amagnetic eld encircling the bus bar in closed loops. The magnetizablecores I I and I2 being in the magnetic field set up by the currentflowing through the central portion 2c of the bus bar, together with thebackstrap 34 and the armature I6, offer a relatively low reluctance pathfor the encircling magnetic lines of force of the magnetic eld. Thearmature I6, being biased in a counterclockwise direction by the coilspring 2l, will be attracted to the pole faces lib and IZb against thebias of the spring 2l when the flux in the magnetic circuit exerts aforce greater than the biasing force of the spring 2l.

The operation of the armature I6 in response to the flux threading themagnetic circuit of the relay may be varied by varying the reluctance ofthe magnetic circuit by including therein the ncnrnagnetic shims 40, orby varying the tension of the spring 2l biasing the rotor assembly. Byvarying the reluctance of the magnetic circuit an approximate range ofcurrent values at which the relay will close its front contacts isestablished and by varying the tension of the coil spring 2l the pick upcurrent value of the relay may be accurately determined.

The coil spring 21 biasing the rotor assembly I3 is a long spring, andthe biasing force exerted thereby may be considered as remainingconstant in any position of the armature from its release position toits full-stroke position. When the magnetic force exerted on thearmature is greater than the biasing force of the coil spring, thearmature will move toward its full-stroke postion, thereby decreasingthe widths of the air gaps between the pole faces of the armature andthe pole pieces. The torque exerted on the armature by the magnetomotiveforce thus increases while the biasing torque of the coil spring remainsconstant, so that the armature moves to its full-stroke position with asnap action. Since the air gaps between the armature and the pole piecesare narrower when the armature is in its full-stroke position than whenin its release position, a lesser magnetomotive force is required tohold the armature in its full-stroke position than to move the armaturefrom its release positiony against the bias of the coil spring. |Thecurrent or pick up value at which the relay will close its frontcontacts is thus greater than the current or release value at which therelay will open its front contacts.

Considering for the moment, a short spring biasing the rotor assembly i3in place of the long spring 21, and a torque exerted on the armature bythe magnetomotive force sufficient to overcome the bias of the shortspring, the movement of the armature from its release position towardits fullstroke position will increase the biasing torque of the shortspring. The decreasing widths of the air gaps between the armature andthe pole pieces will decrease the reluctance of the magnetic circuit sothat an increasing torque is exerted on the armature by themagnetomotive force. The increasing torques exerted on the armature tendto balance each other with the result that the armature creeps to itsfull-stroke position. When the armature is in its full-stroke position,the magnetomotive force acting upon the armature will be at its maximum,but the biasing force of the short spring will also be at its maximum.Thus any small change in the value of the current creating themagnetomotive force will permit the return of the armature to itsrelease position. With a short spring biasing the rotor assembly, thecurrent, or pick up value at which the relay will close its frontcontacts is thus approximately equal to the current, or release value atwhich the relay will open its iront contacts.

In providing an electrical relay having a high ratio of release to pickup value I combine the biasing influences of two springs, a long springsuch as the coil spring 21 described and a short spring such as the flatsprings 2| and 22 which I will now describe in detail; the springarrangement being such that I retain the snap action or a rotor assemblyinfluenced by a long spring and the high ratio of release to pick upvalue of a relay having a rotor assembly inuenced by a short spring, thespring arrangement also providing means whereby the ratio of the releaseto pick up value may be accurately controlled.

To this end, the free ends of the fiat springs 2l and 22 are conned inslots 44a cut in tabs 44 of insulation material. The tabs 44 are securedto threaded blocks 45 which are threaded on the oppositely threaded endsof an adjustment screw 46, the ends of the flat springs being held andtending to bias the armature toward its mid-stroke position. Theadjustment screw 46 is rotatably mounted in the frame legs id and le,the screw being conned in the frame by a sleeve or collar 41 pinned tothe screw between the supporting frame legs (Fig-s. 3 and 4). By turningthe adjustment screw one way or the other, the blocks 45 carrying theconfining tabs 44 may be moved toward or away from each other to Varythe effective lengths of the two flat springs 2| and 22. By varying theeffective lengths of the springs, the stiiness of the two springs isvaried without producing any reaction force which may cause friction andwear at the pivot points.

The general effect of stiffening the flat springs 2! and 22 is toincrease the bias of the rotor assembly toward its mid-stroke position.This biasing eiTect of the two iiat springs tends to reduce the forceexerted by the spiral spring in holding the rotor assembly in itsreleased position with the armature i6 abutting the stops 3 ia, 3 Ib.The restoring force of the spiral spring 27 in returning the rotorassembly from its full-stroke position is increased by the centeringeffect of the two flat springs 2l and 22. As a result of this modulatingaction on the spiral spring torque by the centering torque of the flatsprings, the pick up value of the relay will be reduced since thecentering torque of the flat springs partially offsets the biasingtorque of the coil spring. The release value of the relay will beincreased since the centering torque of the flat springs now aids therestoring force of the coil spring. The adjustment of the effectivelengths of the iiat springs 2| and 22 by the adjustment screw thuscontrols the ratio of release to pick up values of the relay.

The relay mechanism herein described may be advantageously used with abus bar permanently connected in service, any replacement or servicingof the relay being accomplished by handling of the small self-containedrelay unit. The calibration of the relay mechanism is also more easilyeffected, the relay mechanism being removed from the bus bar andreassembled to test coils having a xed number of turns, so that therelay can be calibrated from a low current source. The adjustments ofthe coil spring and of the flat springs of the rotor assembly are alsoadvantageous in that such adjustments of the tension or stiiness of thesprings may be readily and accurately made, the adjustment of theeffective lengths of the two flat springs to vary the ratio of releaseto pick up values of the relay being simpler than methods provided inthe prior art. Such adjustments may readily be made without disassemblyof the relay unit, and may even be made through a cover or shieldsuitably provided with openings for insertion of a screw driver.

Although I have herein shown and described only one form of anelectrical relay embodying my invention, it is understood that variouschanges and modifications may be made therein within the scope of theappended claims without departing from the spirit and scope of myinvention.

Having thus described my invention, what I claim is:

1. In combination, a member mounted for movement between two extremepositions, a rst spring biasing said member toward a positionintermediate the two extreme positions, the bias of said rst springincreasing as said member is moved from the intermediate position towardeither of the two extreme positions, a longer second spring biasing saidmember to one extreme position against the bias of said rst spring, thebias of said second spring remaining substantially uniform throughoutthe range of movement of said member, and means for applying a force ofpredetermined magnitude to move said member from the one extremeposition to the other extreme position, said first and second springscoactng to move said member from the other extreme position when theforce applied to said member is less than the predetermined magnitude.

2. In combination in accordance with claim l in which means are includedto vary the bias of said second spring to vary the magnitude of theforce required to move said member from the one extreme position to theother extreme position.

3. The combination in accordance with claim 2 in which means areincluded to vary the b-ias of said rst spring to vary the ratio of themagnitude of the force applied to said member in its other extremeposition which permits movement of said member from the other extremeposition by said springs, to the magnitude of the force required to movesaid member to the other extreme position.

4. The combination in accordance with claim 3 in which the rst spring isa. flat spring and the longer second spring is a coil spring, and inwhich the means to vary the bias of said rst spring includes a confiningmember for the spring to vary the eective length thereof.

5. In an electrical relay, the combination comprising, a magne'tizablecore structure including a member movable between two extreme positions,and two mechanical force exerting means coacting with said movablemember, each exerting a force of different magnitude on said member; therst of said means tending to move said member to a position intermediateits two extreme positions and the second of said means moving saidmember to one of its extreme positions, said member being moved from theone extreme position to the other extreme position in response tomagnetic flux of a. predetermined level supplied to said core structure,the force exerted by the rst of said means on said member increasing assaid member is moved from the intermediate position toward either of itstwo extreme positions; the force exerted by the second or said means onsaid member being substantially uniform throughout the range of movementor said member; both of said means coasting to move said member from itsother extreme position toward its one extreme position when the magneticflux level supplied to said Core structure falls below the magnetic uxlevel at which said member was moved from its one extreme position toits other extreme position.

6. In an electrical relay, the combination comprising, a magnetizablecore structure including a member movable between two extreme positions,and two springs coacting with said movable member, each spring exertinga force of different magnitude on said member; one of said springstending to bias said member to a position intermediate the two extremepositions, the other of said springs biasing said member to one extremeposition in opposition to the bias of the one spring; said member beingmoved from the one extreme position to the other extreme position inresponse to magnetic flux of a predetermined level supplied to the corestructure; the force exerted by the one spring on said member increasingas said member is moved from the intermediate position toward either ofits extreme positions; the force exerted by the other of said springs onsaid member being substantially uniform throughout the range of movementof the member; both of said springs coacting to move said member fromthe other extreme position toward the one extreme position when thelevel of the magnetic flux supplied to the core structure falls belowthe magnetic flux level at which said member was moved from the oneextreme position to the other extreme position.

7. In an electrical relay, the combination comprising, a magnetizablecore structure including .a member movable between two extremepositions, two Springs coacting with said movable member, each springexerting a force of different magnitude on said member; one of saidsprings tending to bias said member to a position intermediate the twoextreme positions, the other of said springs biasing said member to oneextreme position in opposition to the bias of the one spring, saidmember being moved from the one extreme position to the other extremeposition in response to magnetic ux of a predetermined ,toward the oneextreme level supplied to the core structure; the force exerted by theone spring on said member increasing as said member is moved from theintermediate position toward either of its extreme positions; the forceexerted by the other of said springs on said member being substantiallyuniform throughout the range of movement of the member, both of saidsprings coacting to move said member from the other extreme positionposition when the magnetic flux level supplied the core structure fallsbelow the magnetic ux level at which said member was moved from the oneextreme position to the other extreme position, and means for varyingthe bias of each of said springs to vary the magnetic flux level atwhich said member is moved to its other extreme position and the ratioof the magnetic flux level at which said member is moved from its otherextreme position to the magnetic flux level at which the member is movedto its other extreme position.

8. In an electrical relay, the combination comprising, a magnetizablecore structure including a member movable between two extreme positions,a at spring tending to bias said member to a position intermediate thetwo extreme positions, and a coil spring biasing said member to oneextreme position, said member being moved from the one extreme positionto the other extreme position in response to magnetic flux of apredetermined level supplied to the core structure; the force exerted bythe coil spring on said member being substantially uniform throughoutthe range or movement of the member, the force exerted by the ilatspring on said member increasing as said member is moved from theintermediate position toward either of its extreme positions; both ofsaid springs coacting to move said member from the other extremeposition toward the one extreme position when the magnetic ux level ofthe core structure falls below the magnetic flux level at which themember was moved from the one extreme position to the other extremeposition.

9. In an electrical relay, the combination comprising, a magnetizablecore structure including a member movable between two extreme positions,a. flat spring tending to bias said member to a position intermediatethe two extreme positions, a coil spring biasing said member to oneextreme position, said member being moved from the one extreme positionto the other extreme position in response to magnetic ux of apredetermined level supplied to the core structure; the force exerted bythe coil spring on said member being substantially uniform throughoutthe range of movement of the member, the force exerted by the dat springon said member increasing as said member is moved from the intermediateposition toward either of its extreme positions; both of said springscoacting to move said member from the other extreme position toward theone extreme position when the magnetic iiux level of the core structurefalls below the magnetic flux level at which the member was moved fromthe one eX- treme position to the other extreme position, and means forvarying the bias of each of said springs to vary the magnetic flux levelat which said member is moved from its one extreme position to its otherextreme position and to vary the ratio of the magnetic iiux level atwhich said member is moved from its other extreme position to themagnetic flux level at which the member is moved to its other extremeposition.

10. An electrical relay comprising a nonmagnetic frame member,magnetizable core members secured in said frame, a rotor pivotallymounted in said frame including a magnetizable armature for oscillationbetween two extreme positions, a pair of oppositely extending at springssecured in said rotor, means for confining the free ends of said flatsprings to bias said rotor to a position intermediate the two eXtremepositions, and a coil spring secured at one end in said rotor and at theother end with said frame to bias said rotor to one extreme positionagainst the bias of said iiat springs, said rotor being moved to theother extreme position by said armature in response to magnetic flux ofa predetermined level supplied to said core members, said flat springsand said coil spring coacting to move said rotor from the other extremeposition when the magnetic flux level in said core members falls belowthe magnetic ux level at which said armature was moved to the otherextreme position.

l1. An electrical relay comprising a nonmagnetic frame member,magnetizable core members secured in said frame, a rotor pivotallymounted in said frame including a magnetizable armature for oscillationbetween two extreme positions, a pair of oppositely extending flatsprings secured in said rotor, an adjustment screw conned in said framemember and having oppositely threaded ends, two confining membersthreaded on the ends of said screw and conning the ends of said iiatsprings, the turning of said adjustment screw moving said conningmembers toward and away from each other to vary the effective lengths ofsaid flat springs, said flat springs biasing said rotor to a positionintermediate the two extreme positions, and a coil spring secured at oneend in said rotor and at the other end to said frame to bias said rotorto one extreme position against the bias of said dat springs, said rotorbeing moved to the other extreme position by said armature in responseto 1 magnetic ux of a predetermined level supplied to said core members,said at springs and said coil spring coacting to move said rotor fromthe other extreme position when the magnetic iiux level in said coremembers falls below the magnetic flux level at which said armature wasmoved to the other extreme position.

l2. An electrical relay comprising a nonmagnetic frame member,magnetizable core members secured in said frame, a rotor pivotallymounted in said frame including a magnetizable armature for oscillationbetween two extreme positions, a pair of oppositely extending flatsprings secured in said rotor, an adjustment screw coniined in saidframe member and having oppositely threaded ends, two conning membersthreaded on the ends of said screw and confining the ends of said iiatsprings, the turning of said adjustment screw moving said confiningmembers toward and away from each other to vary the effective lengths ofsaid at springs, said flat springs biasing said rotor to a positionintermediate the two extreme positions, a coil spring secured at one endto said rotor; an arm pivoted to said frame member, the end of said armbeing secured to the other end of said coil spring, a second adjustmentscrew threaded in said frame for abutting the end of said arm, theturning of said second adjustment screw varying the tension ci said coilspring, said coil spring biasing said rotor to one extreme positionagainst the bias of said flat springs, said rotor being oscillated tothe other extreme position by said armature in response to magnetic iluxof a predetermined level supplied to said core members, the tension ofsaid coil spring determining the magnetic flux level at which saidarmature is moved to the other extreme position; said flat springs andsaid coil spring coacting to move said rotor from the other extremeposition when the magnetic flux level falls below the magnetic ux levelat which said armature was moved to the other extreme position; thevariation of the effective lengths of the flat springs varying the ratioof the magnetic flux level at which the rotor is moved from the otherextreme position to the magnetic ilux level at which the rotor is movedto the other extreme position.

13. An electrical relay operable in response to current flowing in a busbar comprising a nonmagnetic frame member, magnetizable core memberssecured in said frame and adapted to be positioned in the magnetic eldestablished by the current flowing in said bus bar, a rotor ofinsulation material pivotally mounted in said frame including amagnetizable armature for oscillation between two extreme positions, apair of oppositely extending fiat springs secured in said rotor, meansfor conning the free ends of said fiat springs, said fiat springsbiasing said rotor to a position intermediate the two extreme positions,a coil spring secured at one end to said rotor and at the other end withsaid frame member to bias said rotor to one eXtreme position against thebias of said at springs; said rotor being moved to the other extremeposition by said armature in response to magnetic flux threading saidarmature and core members of a predetermined magnitude determined by thevalue of the current traversing the bus bar, said iiat springs and saidcoil spring coacting to move said rotor from the other eXtreme positionwhen the value of the current through the bus bar falls below the valueof the bus bar current at which the rotor is moved to the other eXtremeposition, means for varying the bias of said coil spring to vary thevalue of the current at which said rotor is moved to the other eXtremeposition, and means for moving said confining means on the ends of saidflat springs toward and away from each other to vary the effectivelengths of the flat springs to vary the ratio of the value of thecurrent at which the rotor is moved from the other extreme position tothe value of the current at which the rotor is moved to the otherextreme position.

14. ln combination, a member pivoted for osciliation between two extremepositions; two oppositely extending flat springs, each secured at oneend to said member; a coniined adjustment screw coextensive with the atsprings and oppositely threaded at each end, and a confining memberthreaded on each end of said screw and confining the free end of a flatspring, the turning of said screw moving said conning members toward andaway from each other to vary the effective lengths of said at springs,said flat springs biasing said member to a position intermediate the twoextreme positions.

15. In combination, a member pivoted for oscillation between two extremepositions; two oppositely extending at springs, each secured at one endto said member; a coniined adjustment screw coextensive with the iiatsprings and oppositely threaded at each end, a coniining member threadedon each end of said screw and confining the free end of a flat spring,the turning of said screw moving said conning members toward and awayfrom each other to vary the effective lengths of said fiat springs, saidnat springs biasing said member to a position intermediate the twoextreme positions, a coil spring secured at one end to said member, anarm pivoted at one end and having its free end secured to the free endof said coil spring, a second adjustment screw abutting the free end ofsaid arm to vary the tension of said coil spring, said coil springbiasing said member to one extreme position, and means for applying aforce to said member to move said member from the one extreme positionto the other extreme position, said coil spring and said nat springsmoving said member from the other extreme position when the magnitude ofthe force required to move said member to its other extreme position isdecreased.

15. In an electrical relay operable in response to current flowing in abus bar having two spaced openings therein, the combination comprising abase plate of insulation material, a nonmagnetic frame member secured tosaid base plate, two magnetizable core members secured in said framemember and passing through said base plate, a rotor assembly pivotallymounted in said frame member including a magnetizable armature foroscillation between two extreme positions; said core members beingadapted to extend through the bus bar openings when said base plateabuts the bus bar, a magnetizable backstrapfor the ends of said coremembers extendingI through the bus bar openings, a cover of insulationmaterial accommodating said backstrap, means for clamping said cover andsaid base plate to said bus bar, and resilient means interposed betweensaid cover and said backstrap to bias said backstrap against theextending ends of said core members.

17. An electrical relay operable in response to current owing in a busbar having two slots cut into the opposite edges thereof, comprising abase plate of insulation material, a nonmagnetic frame secured to saidbase plate, two magnetizable core members secured in said frame memberand extending through said base plate, a rotor of insulation materialpivotally mounted in said frame including a magnetizable armature foroscillation between two extreme positions, a pair of oppositelyextending flat springs secured in said rotor, means for connning thefree ends of said flat springs, said flat springs biasing said rotor toa position intermediate the twoextreme positions, a coil spring securedat one end to said rotor and at the other end with said frame member tobias said rotor to one extreme position against the bias of said fiatsprings; said core members being adapted to extend through the bus barslots when the base plate abuts the bus bar, a magnetizable backstrapfor the ends of said core members extending through the bus bar slots, acover of insulation material accommodating said backstrap, means forclamping said base plate and said cover to said bus bar, and resilientmeans interposed between said cover and said bus bar to bias saidbackstrap against the extending ends of said core members; said rotorbeing moved to the other extreme position by said armature in responseto magnetic flux threading said armature backstrap and core members of apredetermined magnitude determined by the value of the currenttraversing the bus bar, said nat springs and said coil spring coactingto move said rotor from the other extreme position when 14 the value ofthe current through the bus bar falls below the value of the bus barcurrent at which the rotor was moved to the other extreme position.

18. An electrical relay operable in response to current iowing in a busbar having two slots cut into the opposite edges thereof, comprising abase plate of insulation material, a nonmagnetic frame secured to saidbase plate, two magnetizable core members secured in said frame memberand extending through said base plate, a rotor of insulation materialpivotally mounted in said frame including a magnetizable armature foroscillation between two extreme positions, a pair of oppositelyextending flat springs secured in said rotor, means for conning the freeends of said flat springs, said flat springs biasing said rotor to aposition intermediate the two extreme positions, a coil spring securedat one end to said rotor and at the other end with said frame member tobias said rotor to one extreme position against the bias of said flatsprings; said core members being adapted to extend through the bus barslots when the base plate abuts the bus bar, a magnetizable backstrapfor the ends of said core members extending through the bus bar slots, acover of insulation material accommodating said backstrap, means forclamping said base plate and said cover to said bus bar, resilient meansinterposed between said cover and said bus bar to bias said backstrapagainst the extending ends of said core members; said rotor being movedto the other extreme position by said armature in response to magneticflux threading said armature, backstrap and core members of apredetermined magnitude determined by the value of the currenttraversing the bus bar, said fiat springs and said coil spring coactingto move said rotor from the other extreme position when the value of thecurrent through the bus bar falls below the value of the bus bar currentat which the rotor is moved t0 the other extreme position, means forvarying the bias of said coil spring to vary the value of the current atwhich said rotor is moved to the other extreme position, and means formoving said confining means on the ends of said at springs toward andaway from each other to vary the eiective lengths of the flat springs tovary the ratio of the value of the current at which the rotor is movedfrom the other extreme position to the value of the current at which therotor is moved to the other extreme position.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 786,696 Vreeland Apr. 4, 1905 940,319 Hoyt 1 Nov. 16, 19092,140,604 Snavely Dec. 20, 1938 2,256,653 Snavely Sept. 23, 19412,283,270 Laurenson May 19, 1942 2,294,484 Snavely Sept. l, 19422,334,514 Snavely Nov. 16, 1943 2,428,784 Cole Oct. 14, 1947 2,584,749Snavely Feb. 5, 1952

